Olefin based polymers are widely used in various applications due to their being chemically inert, having low density, and low cost. However, polyolefins present non-polar surfaces to which more polar materials may not readily adhere. As such, to apply a layer of paint, adhesive, or the like to a surface comprised of an olefin based polymer such as polypropylene, a tie layer or other adhesion promoter may be required. In addition, adhesive compositions comprising olefin based polymers may not readily adhere to polar substrates such as paper, cardboard and the like.
To provide effective adhesion between polar and non-polar substances, good bonding strength and/or intimate integrity between the materials must be achieved. A tie layer or adhesion promoter may provide a bridge between a non-polar surface such as isotactic polypropylene, and a more polar surface such as Mylar® (Dupont), or paper. However, tie layers and adhesion promoters may require blends having performance over very limited criteria. Tie layers and adhesion promoters may also comprise components which may add expense and complexity to a formulation, and/or may be difficult to produce. Such factors for tie layers and adhesion promoters may render a particular formulation unsuitable for a particular use.
For example, patent application WO 02/20644 discloses structures comprising a polypropylene layer and a tie consisting of a polypropylene backbone on which polymethylmethacrylate (“PMMA”) grafts are attached and a polyvinyldifluoride (“PVDF”) layer. To manufacture the tie, maleic anhydride is grafted onto a polypropylene backbone and then this backbone carrying the maleic anhydride is made to react with a copolymer of methyl methacrylate (“MMA”) and hydroxyethyl methacrylate (“HEMA”). The reaction between maleic anhydride and HEMA allows the PMMA graft to be fixed. However, this reaction is not easily carried out, and the MMA-HEMA copolymer may present difficulties in manufacture.
Patent application JP 08336937 A, published on Dec. 24, 1996, discloses structures similar to those above, but the tie is a graft copolymer obtained by solution polymerization of a mixture of MMA, acrylonitrile and styrene in the presence of an elastomer chosen from hydrogenated SBS (copolymers having polystyrene blocks and polybutadiene blocks), hydrogenated polybutadienes and ethylene-propylene rubbers. While this tie layer may prove facile in manufacture, the structures have insufficient properties, in particular in the presence of hydrocarbon solvents.
U.S. patent application 20040023037 is directed to a tie layer for making a polyolefin layer adhere to a PVDF layer. The tie layer comprising a graft polymer obtained by polymerization of MMA in the presence of preferably very low density polyethylene, or an ethylene-alkyl (meth)acrylate copolymer. This polymerization may take place in an extruder with or without any solvent, but may lack the integrity of more demanding conditions.
EP 033 220 is directed to graft polymers obtained by polymerization in an extruder of MMA in the presence of a polymer chosen from ethylene-propylene rubber, and blends of ethylene-propylene rubber with low density polyethylene, ethylene vinyl acetate copolymer, and blends thereof. These graft polymers may be limited in use as impact modifiers in polyvinylchloride (“PVC”).
U.S. Pat. No. 4,476,283 discloses graft polymers obtained by polymerization in an extruder of MMA, styrene or acrylonitrile in the presence of an ethylene-propylene-diene copolymer/ethylene-propylene rubber blend. These graft polymers may be limited to use as a blend with styrene-butadiene rubbers or nitrile-butadiene rubbers.
There thus remains a need for an adhesive, an adhesive promoter, or a tie layer material that will intimately bond to both polar and non-polar substrates, preferably one that exhibits a superior durability of bond strength under various temperature conditions in the presence of aggressive products or conditions which is easily produced and readily available.